Plasma-assisted processing in a manufacturing line

ABSTRACT

Methods and apparatus are provided for plasma-assisted processing multiple work pieces in a manufacturing line. In one embodiment, the method can include placing the work pieces in movable carriers, moving the carriers on a conveyor into an irradiation zone, flowing a gas into the irradiation zone, igniting the gas in the irradiation zone to form a plasma (e.g., by subjecting the gas to electromagnetic radiation in the presence of a plasma catalyst), sustaining the plasma for a period of time sufficient to at least partially plasma process at least one of the work pieces in the irradiation zone, and advancing the conveyor to move the at least one plasma-processed work piece out of the irradiation zone. Various types of plasma catalysts are also provided.

CROSS-REFERENCE OF RELATED APPLICATIONS

Priority is claimed to U.S. Provisional Patent Application No.60/378,693, filed May 8, 2002, No. 60/430,677, filed Dec. 4, 2002, andNo. 60/435,278, filed Dec. 23, 2002, all of which are fully incorporatedherein by reference.

FIELD OF THE INVENTION

This invention relates to methods and apparatus for plasma-assistedprocessing of work pieces in a manufacturing line.

BACKGROUND OF THE INVENTION

Plasmas can be used to assist in a number of processes, including thejoining and heat-treating of materials. However, igniting, modulating,and sustaining plasmas for these purposes can be difficult for a numberof reasons.

For example, it is known that a plasma can be ignited in a cavity bydirecting a large amount of microwave radiation into the cavitycontaining a gas. If the radiation intensity is large enough, the plasmacan ignite spontaneously. However, radiation sources capable ofsupplying such large intensities can have several disadvantages; theycan be expensive, heavy, bulky, and energy-consuming. Moreover, theselarge radiation sources normally require large electrical powersupplies, which can have similar disadvantages.

One way of igniting a plasma with a lower radiation intensity is toreduce the pressure in the cavity. However, vacuum equipment, which canbe used to reduce this pressure, can limit manufacturing flexibility,especially as the plasma chambers become large and especially in thecontext of manufacturing lines.

A sparking device can also be used to ignite a plasma using a lowerradiation intensity. Such a device, however, only sparks periodicallyand therefore can only ignite a plasma periodically, sometimes causingan ignition lag. Moreover, conventional sparking devices are normallypowered with electrical energy, limiting their use and position in manymanufacturing environments.

BRIEF SUMMARY OF A FEW ASPECTS OF THE INVENTION

A method of plasma-assisted processing a plurality of work pieces can beprovided. In one embodiment, a method of plasma-assisted processing aplurality of work pieces is provided. The method can includesequentially conveying a plurality of work pieces into an irradiationzone, flowing a gas into the irradiation zone, igniting the gas in theirradiation zone to form a plasma, sustaining the plasma for a period oftime sufficient to at least partially plasma process at least one of thework pieces in the irradiation zone, and sequentially conveying theplurality of work pieces out of the irradiation zone.

In another embodiment, the method can include placing each of theplurality of work pieces in a plurality of movable carriers,sequentially moving each of the movable carriers on a conveyor into anirradiation zone, flowing a gas into the irradiation zone, igniting thegas in the irradiation zone to form a plasma, sustaining the plasma fora period of time sufficient to at least partially plasma process atleast one of the work pieces in the irradiation zone, and advancing theconveyor to move the at least one plasma-processed work piece out of theirradiation zone.

Apparatus for plasma-assisted processing a plurality of work pieces mayalso be provided. In one embodiment, an apparatus can include aradiation source, a radiation housing through which radiation passesfrom the source, a conveyor for sequentially moving the work pieces intoand out of an irradiation zone adjacent the housing in the presence of aplasma. The apparatus may also include a gas inlet for conveying gasinto the irradiation zone to enable plasma formation in the irradiationzone.

A plasma catalyst for initiating, modulating, and sustaining a plasma isalso provided. The catalyst can be passive or active. A passive plasmacatalyst can include any object capable of inducing a plasma bydeforming a local electric field (e.g., an electromagnetic field)consistent with this invention, without necessarily adding additionalenergy. An active plasma catalyst, on the other hand, is any particle orhigh energy wave packet capable of transferring a sufficient amount ofenergy to a gaseous atom or molecule to remove at least one electronfrom the gaseous atom or molecule in the presence of electromagneticradiation. In both cases, a plasma catalyst can improve, or relax, theenvironmental conditions required to ignite a plasma.

Additional plasma catalysts, and methods and apparatus for igniting,modulating, and sustaining a plasma for producing a gas consistent withthis invention are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the invention will be apparent upon consideration ofthe following detailed description, taken in conjunction with theaccompanying drawings, in which like reference characters refer to likeparts throughout, and in which:

FIG. 1 shows a schematic diagram of an illustrative plasma-assisted gasproduction system consistent with this invention;

FIG. 1A shows an illustrative embodiment of a portion of aplasma-assisted gas production system for adding a powder plasmacatalyst to a plasma cavity for igniting, modulating, or sustaining aplasma in a cavity consistent with this invention;

FIG. 2 shows an illustrative plasma catalyst fiber with at least onecomponent having a concentration gradient along its length consistentwith this invention;

FIG. 3 shows an illustrative plasma catalyst fiber with multiplecomponents at a ratio that varies along its length consistent with thisinvention;

FIG. 4 shows another illustrative plasma catalyst fiber that includes acore under layer and a coating consistent with this invention;

FIG. 5 shows a cross-sectional view of the plasma catalyst fiber of FIG.4, taken from line 5-5 of FIG. 4, consistent with this invention;

FIG. 6 shows an illustrative embodiment of another portion of a plasmasystem including an elongated plasma catalyst that extends throughignition port consistent with this invention;

FIG. 7 shows an illustrative embodiment of an elongated plasma catalystthat can be used in the system of FIG. 6 consistent with this invention;

FIG. 8 shows another illustrative embodiment of an elongated plasmacatalyst that can be used in the system of FIG. 6 consistent with thisinvention;

FIG. 9 shows an illustrative embodiment of a portion of aplasma-assisted processing system for directing ionizing radiation intoa radiation chamber consistent with this invention;

FIG. 10 shows a perspective view of illustrative apparatus forplasma-assisted processing of multiple work pieces consistent with thisinvention;

FIG. 11 shows another perspective view of the illustrative apparatus ofFIG. 10 consistent with this invention;

FIG. 12 shows a top plan view of an illustrative conveyor that can beused with the apparatus of FIG. 10 consistent with this invention;

FIG. 13 shows a cross-sectional view of the illustrative conveyor ofFIG. 12, taken along line 13-13 of FIG. 12, along with variousadditional components and work pieces, consistent with this invention;

FIG. 14 shows a cross-sectional view of another illustrative conveyorwith recesses in which work pieces can be placed consistent with thisinvention; and

FIG. 15 shows a flow-chart for an illustrative method ofplasma-processing a plurality of work pieces consistent with thisinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

This invention relates to methods and apparatus for plasma-assistedprocessing in a manufacturing line and can be used to lower energy costsand increase manufacturing flexibility.

The following commonly owned, concurrently filed U.S. patentapplications are hereby incorporated by reference in their entireties:U.S. patent application Ser. No. 10/______ (Atty. Docket No. 1837.0008),Ser. No. 10/______ (Atty. Docket No. 1837.0009), Ser. No. 10/______(Atty. Docket No. 1837.0010), Ser. No. 10/______ (Atty. Docket No.1837.0011), Ser. No. 10/______ (Atty. Docket No. 1837.0012), Ser. No.10/______ (Atty. Docket No. 1837.0013), Ser. No. 10/______ (Atty. DocketNo. 1837.0015), Ser. No. 10/______ (Atty. Docket No. 1837.0016), Ser.No. 10/______ (Atty. Docket No. 1837.0017), Ser. No. 101/______ (Atty.Docket No. 1837.0018), Ser. No. 10/______ (Atty. Docket No. 1837.0020),Ser. No. 10/______ (Atty. Docket No. 1837.0021), Ser. No. 10/______(Atty. Docket No. 1837.0023), Ser. No. 10/______ (Atty. Docket No.1837.0024), Ser. No. 10/______ (Atty. Docket No. 1837.0025), Ser. No.10/______ (Atty. Docket No. 1837.0026), Ser. No. 10/______ (Atty. DocketNo. 1837.0028), Ser. No. 10/______ (Atty. Docket No. 1837.0029), Ser.No. 10/______ (Atty. Docket No. 1837.0030), Ser. No. 10/______ (Atty.Docket No. 1837.0032), and Ser. No. 10/______ (Atty. Docket No.1837.0033).

Illustrative Plasma System

FIG. 1 shows illustrative plasma system 10 consistent with one aspect ofthis invention. In this embodiment, cavity 12 is formed in a vessel thatis positioned inside radiation chamber (i.e., applicator) 14. In anotherembodiment (not shown), vessel 12 and radiation chamber 14 are the same,thereby eliminating the need for two separate components. The vessel inwhich cavity 12 is formed can include one or more radiation-transmissiveinsulating layers to improve its thermal insulation properties withoutsignificantly shielding cavity 12 from the radiation. As described morefully below, system 10 can be used to generate a plasma and can beincluded in a manufacturing line consistent with this invention.

In one embodiment, cavity 12 is formed in a vessel made of ceramic. Dueto the extremely high temperatures that can be achieved with plasmasconsistent with this invention, a ceramic capable of operating at about3,000 degrees Fahrenheit can be used. The ceramic material can include,by weight, 29.8% silica, 68.2% alumina, 0.4% ferric oxide, 1% titania,0.1% lime, 0.1% magnesia, 0.4% alkalies, which is sold under Model No.LW-30 by New Castle Refractories Company, of New Castle, Pa. It will beappreciated by those of ordinary skill in the art, however, that othermaterials, such as quartz, and those different from the one describedabove, can also be used consistent with the invention.

In one successful experiment, a plasma was formed in a partially opencavity inside a first brick and topped with a second brick. The cavityhad dimensions of about 2 inches by about 2 inches by about 1.5 inches.At least two holes were also provided in the brick in communication withthe cavity: one for viewing the plasma and at least one hole forproviding the gas. The size of the cavity can depend on the desiredplasma process being performed. Also, the cavity can at least beconfigured to prevent the plasma from rising/floating away from theprimary processing region.

Cavity 12 can be connected to one or more gas sources 24 (e.g., a sourceof argon, nitrogen, hydrogen, xenon, krypton) by line 20 and controlvalve 22, which may be powered by power supply 28. Line 20 may be tubing(e.g., between about 1/16 inch and about ¼ inch, such as about ⅛″), butcould be any device capable of delivering gas. Also, if desired, avacuum pump can be connected to the chamber to remove fumes that may begenerated during plasma processing. In one embodiment, gas can flow inand/or out of cavity 12 through one or more gaps in a multi-part vessel.Thus, gas ports consistent with this invention need not be distinctholes and can take on other forms as well, such as many smalldistributed holes.

A radiation leak detector (not shown) was installed near source 26 andwaveguide 30 and connected to a safety interlock system to automaticallyturn off the radiation (e.g., microwave) power supply if a leak above apredefined safety limit, such as one specified by the FCC and/or OSHA(e.g., 5 mW/cm²), was detected.

Radiation source 26, which may be powered by electrical power supply 28,can direct radiation energy into chamber 14 through one or morewaveguides 30 or by using a coaxial cable. It will be appreciated bythose of ordinary skill in the art that source 26 can be connecteddirectly to cavity 12 or chamber 14, thereby eliminating waveguide 30.The radiation energy entering cavity 12 is used to ignite a plasmawithin the cavity. This plasma can be substantially sustained andconfined to the cavity by coupling additional radiation with thecatalyst

Radiation energy can be supplied through circulator 32 and tuner 34(e.g., 3-stub tuner). Tuner 34 can be used to minimize the reflectedpower as a function of changing ignition or processing conditions,especially after the plasma has formed because microwave power, forexample, will be strongly absorbed by the plasma.

As explained more fully below, the location of radiation-transmissivecavity 12 in chamber 14 may not be critical if chamber 14 supportsmultiple modes, and especially when the modes are continually orperiodically mixed. As also explained more fully below, motor 36 can beconnected to mode-mixer 38 for making the time-averaged radiation energydistribution substantially uniform throughout chamber 14. Furthermore,window 40 (e.g., a quartz window) can be disposed in one wall of chamber14 adjacent to cavity 12, permitting temperature sensor 42 (e.g., anoptical pyrometer) to be used to view a process inside cavity 12. In oneembodiment, the optical pyrometer output can increase from zero volts asthe temperature rises to within the tracking range.

Sensor 42 can develop output signals as a function of the temperature orany other monitorable condition associated with a work piece (not shown)within cavity 12 and provide the signals to controller 44. Dualtemperature sensing and heating, as well as automated cooling rate andgas flow controls can also be used. Controller 44 in turn can be used tocontrol operation of power supply 28, which can have one outputconnected to source 26 as described above and another output connectedto valve 22 to control gas flow into cavity 12.

The invention may be practiced with microwave sources at, for example,both 915 MHz and 2.45 GHz provided by Communications and PowerIndustries (CPI), although radiation having any frequency less thanabout 333 GHz can be used. The 2.45 GHz system provided continuouslyvariable microwave power from about 0.5 kilowatts to about 5.0kilowatts. A 3-stub tuner allowed impedance matching for maximum powertransfer and a dual directional coupler was used to measure forward andreflected powers. Also, optical pyrometers were used for remote sensingof the sample temperature.

As mentioned above, radiation having any frequency less than-about 333GHz can be used consistent with this invention. For example,frequencies, such as power line frequencies (about 50 Hz to about 60Hz), can be used, although the pressure of the gas from which the plasmais formed may be lowered to assist with plasma ignition. Also, any radiofrequency or microwave frequency can be used consistent with thisinvention, including frequencies greater than about 100 kHz. In mostcases, the gas pressure for such relatively high frequencies need not belowered to ignite, modulate, or sustain a plasma, thereby enabling manyplasma-assisted processes to occur at atmospheric pressures and above inany manufacturing environment.

The equipment was computer controlled using LabView 6i software, whichprovided real-time temperature monitoring and microwave power control.Noise was reduced by using sliding averages of suitable number of datapoints. Also, to improve speed and computational efficiency, the numberof stored data points in the buffer array were limited by usingshift-registers and buffer-sizing techniques. The pyrometer measured thetemperature of a sensitive area of about 1 cm² ₁ which was used tocalculate an average temperature. The pyrometer sensed radiantintensities at two wavelengths and fit those intensities using Planck'slaw to determine the temperature. It will be appreciated, however, thatother devices and methods for monitoring and controlling temperature arealso available and can be used consistent with this invention. Forexample, control software that can be used consistent with thisinvention is described in commonly owned, concurrently filed U.S. patentapplication Ser. No. 10/______ (Attorney Docket No. 1837.0033), which ishereby incorporated by reference in its entirety.

Chamber 14 had several glass-covered viewing ports with radiationshields and one quartz window for pyrometer access. Several ports forconnection to a vacuum pump and a gas source were also provided,although not necessarily used.

System 10 also included a closed-loop deionized water cooling system(not shown) with an external heat exchanger cooled by tap water. Duringoperation, the deionized water first cooled the magnetron, then theload-dump in the circulator (used to protect the magnetron), and finallythe radiation chamber through water channels welded on the outer surfaceof the chamber.

Plasma Catalysts

A plasma catalyst consistent with this invention can include one or moredifferent materials and may be either passive or active. A plasmacatalyst can be used, among other things, to ignite, modulate, and/orsustain a plasma at a gas pressure that is less than, equal to, orgreater than atmospheric pressure.

One method of forming a plasma consistent with this invention caninclude subjecting a gas in a cavity to electromagnetic radiation havinga frequency less than about 333 GHz in the presence of a passive plasmacatalyst. A passive plasma catalyst consistent with this invention caninclude any object capable of inducing a plasma by deforming a localelectric field (e.g., an electromagnetic field) consistent with thisinvention, without necessarily adding additional energy through thecatalyst, such as by applying an electric voltage to create a spark.

A passive plasma catalyst consistent with this invention can also be anano-particle or a nano-tube. As used herein, the term “nano-particle”can include any particle having a maximum physical dimension less thanabout 100 nm that is at least electrically semi-conductive. Also, bothsingle-walled and multi-walled carbon nanotubes, doped and undoped, canbe particularly effective for igniting plasmas consistent with thisinvention because of their exceptional electrical conductivity andelongated shape. The nanotubes can have any convenient length and can bea powder fixed to a substrate. If fixed, the nanotubes can be orientedrandomly on the surface of the substrate or fixed to the substrate(e.g., at some predetermined orientation) while the plasma is ignited orsustained.

A passive plasma catalyst can also be a powder consistent with thisinvention, and need not comprise nano-particles or nano-tubes. It can beformed, for example, from fibers, dust particles, flakes, sheets, etc.When in powder form, the catalyst can be suspended, at leasttemporarily, in a gas. By suspending the powder in the gas, the powdercan be quickly dispersed throughout the cavity and more easily consumed,if desired.

In one embodiment, the powder catalyst can be carried into the cavityand at least temporarily suspended with a carrier gas. The carrier gascan be the same or different from the gas that forms the plasma. Also,the powder can be added to the gas prior to being introduced to thecavity. For example, as shown in FIG. 1A, radiation source 52 can supplyradiation to radiation cavity 55, in which plasma cavity 60 is placed.Powder source 65 can provide catalytic powder 70 into gas stream 75. Inan alternative embodiment, powder 70 can be first added to cavity 60 inbulk (e.g., in a pile) and then distributed in the cavity in any numberof ways, including flowing a gas through or over the bulk powder. Inaddition, the powder can be added to the gas for igniting, modulating,or sustaining a plasma by moving, conveying, drilling, sprinkling,blowing, or otherwise, feeding the powder into or within the cavity.

In one experiment, a plasma was ignited in a cavity by placing a pile ofcarbon fiber powder in a copper pipe that extended into the cavity.Although sufficient radiation was directed into the cavity, the copperpipe shielded the powder from the radiation and no plasma ignition tookplace. However, once a carrier gas began flowing through the pipe,forcing the powder out of the pipe and into the cavity, and therebysubjecting the powder to the radiation, a plasma was nearlyinstantaneously ignited in the cavity.

A powder plasma catalyst consistent with this invention can besubstantially non-combustible, thus it need not contain oxygen or burnin the presence of oxygen. Thus, as mentioned above, the catalyst caninclude a metal, carbon, a carbon-based alloy, a carbon-based composite,an electrically conductive polymer, a conductive silicone elastomer, apolymer nanocomposite, an organic-inorganic composite, and anycombination thereof.

Also, powder catalysts can be substantially uniformly distributed in theplasma cavity (e.g., when suspended in a gas), and plasma ignition canbe precisely controlled within the cavity. Uniform ignition can beimportant in certain applications, including those applicationsrequiring brief plasma exposures, such as in the form of one or morebursts. Still, a certain amount of time can be required for a powdercatalyst to distribute itself throughout a cavity, especially incomplicated, multi-chamber cavities. Therefore, consistent with anotheraspect of this invention, a powder catalyst can be introduced into thecavity through a plurality of ignition ports to more rapidly obtain amore uniform catalyst distribution therein (see below).

In addition to powder, a passive plasma catalyst consistent with thisinvention can include, for example, one or more microscopic ormacroscopic fibers, sheets, needles, threads, strands, filaments, yarns,twines, shavings, slivers, chips, woven fabrics, tape, whiskers, or anycombination thereof. In these cases, the plasma catalyst can have atleast one portion with one physical dimension substantially larger thananother physical dimension. For example, the ratio between at least twoorthogonal dimensions can be at least about 1:2, but could be greaterthan about 1:5, or even greater than about 1:10.

Thus, a passive plasma catalyst can include at least one portion ofmaterial that is relatively thin compared to its length. A bundle ofcatalysts (e.g., fibers) may also be used and can include, for example,a section of graphite tape. In one experiment, a section of tape havingapproximately thirty thousand strands of graphite fiber, each about 2-3microns in diameter, was successfully used. The number of fibers in andthe length of a bundle are not critical to igniting, modulating, orsustaining the plasma. For example, satisfactory results have beenobtained using a section of graphite tape about one-quarter inch long.One type of carbon fiber that has been successfully used consistent withthis invention is sold under the trademark Magnamite®, Model No.AS4C-GP3K, by the Hexcel Corporation, of Anderson, S.C. Also,silicon-carbide fibers have been successfully used.

A passive plasma catalyst consistent with another aspect of thisinvention can include one or more portions that are, for example,substantially spherical, annular, pyramidal, cubic, planar, cylindrical,rectangular or elongated.

The passive plasma catalysts discussed above can include at least onematerial that is at least electrically semi-conductive. In oneembodiment, the material can be highly conductive. For example, apassive plasma catalyst consistent with this invention can include ametal, an inorganic material, carbon, a carbon-based alloy, acarbon-based composite, an electrically conductive polymer, a conductivesilicone elastomer, a polymer nanocomposite, an organic-inorganiccomposite, or any combination thereof. Some of the possible inorganicmaterials that can be included in the plasma catalyst include carbon,silicon carbide, molybdenum, platinum, tantalum, tungsten, carbonnitride, and aluminum, although other electrically conductive inorganicmaterials may work just as well.

In addition to one or more electrically conductive materials, a passiveplasma catalyst consistent with this invention can include one or moreadditives (which need not be electrically conductive). As used herein,the additive can include any material that a user wishes to add to theplasma. Therefore, the catalyst can include the additive itself, or itcan include a precursor material that, upon decomposition, can form theadditive. Thus, the plasma catalyst can include one or more additivesand one or more electrically conductive materials in any desirableratio, depending on the ultimate desired composition of the plasma andthe process using the plasma.

The ratio of the electrically conductive components to the additives ina passive plasma catalyst can vary over time while being consumed. Forexample, during ignition, the plasma catalyst could desirably include arelatively large percentage of electrically conductive components toimprove the ignition conditions. On the other hand, if used whilesustaining the plasma, the catalyst could include a relatively largepercentage of additives. It will be appreciated those of ordinary skillin the art that the component ratio of the plasma catalyst used toignite and sustain the plasma could be the same.

A predetermined ratio profile can be used to simplify many plasmaprocesses. In many conventional plasma processes, the components withinthe plasma are added as necessary, but such addition normally requiresprogrammable equipment to add the components according to apredetermined schedule. However, consistent with this invention, theratio of components in the catalyst can be varied, and thus the ratio ofcomponents in the plasma itself can be automatically varied. That is,the ratio of components in the plasma at any particular time can dependon which of the catalyst portions is currently being consumed by theplasma. Thus, the catalyst component ratio can be different at differentlocations within the catalyst And, the current ratio of components in aplasma can depend on the portions of the catalyst currently and/orpreviously consumed, especially when the flow rate of a gas passingthrough the plasma chamber is relatively slow.

A passive plasma catalyst consistent with this invention can behomogeneous, inhomogeneous, or graded. Also, the plasma catalystcomponent ratio can vary continuously or discontinuously throughout thecatalyst. For example, in FIG. 2, the ratio can vary smoothly forming agradient along a length of catalyst 100. Catalyst 100 can include astrand of material that includes a relatively low concentration of acomponent at section 105 and a continuously increasing concentrationtoward section 110.

Alternatively, as shown in FIG. 3, the ratio can vary discontinuously ineach portion of catalyst 120, which includes, for example, alternatingsections 125 and 130 having different concentrations. It will beappreciated that catalyst 120 can have more than two section types.Thus, the catalytic component ratio being consumed by the plasma canvary in any predetermined fashion. In one embodiment, when the plasma ismonitored and a particular additive is detected, further processing canbe automatically commenced or terminated.

Another way to vary the ratio of components in a sustained plasma is byintroducing multiple catalysts having different component ratios atdifferent times or different rates. For example, multiple catalysts canbe introduced at approximately the same location or at differentlocations within the cavity. When introduced at different locations, theplasma formed in the cavity can have a component concentration gradientdetermined by the locations of the various catalysts. Thus, an automatedsystem can include a device by which a consumable plasma catalyst ismechanically inserted before and/or during plasma igniting, modulating,and/or sustaining.

A passive plasma catalyst consistent with this invention can also becoated. In one embodiment, a catalyst can include a substantiallynon-electrically conductive coating deposited on the surface of asubstantially electrically conductive material. Alternatively, thecatalyst can include a substantially electrically conductive coatingdeposited on the surface of a substantially electrically non-conductivematerial. FIGS. 4 and 5, for example, show fiber 140, which includesunderlayer 145 and coating 150. In one embodiment, a plasma catalystincluding a carbon core is coated with nickel to prevent oxidation ofthe carbon.

A single plasma catalyst can also include multiple coatings. If thecoatings are consumed during contact with the plasma, the coatings couldbe introduced into the plasma sequentially, from the outer coating tothe innermost coating, thereby creating a time-release mechanism. Thus,a coated plasma catalyst can include any number of materials, as long asa portion of the catalyst is at least electrically semi-conductive.

Consistent with another embodiment of this invention, a plasma catalystcan be located entirely within a radiation cavity to substantiallyreduce or prevent radiation energy leakage. In this way, the plasmacatalyst does not electrically or magnetically couple with the vesselcontaining the cavity or to any electrically conductive object outsidethe cavity. This prevents sparking at the ignition port and preventsradiation from leaking outside the cavity during the ignition andpossibly later if the plasma is sustained. In one embodiment, thecatalyst can be located at a tip of a substantially electricallynon-conductive extender that extends through an ignition port.

FIG. 6, for example, shows radiation chamber 160 in which plasma cavity165 is placed. Plasma catalyst 170 is elongated and extends throughignition port 175. As shown in FIG. 7, and consistent with thisinvention, catalyst 170 can include electrically conductive distalportion 180 (which is placed in chamber 160) and electricallynon-conductive portion 185 (which is placed substantially outsidechamber 160, but can extend somewhat into chamber 160). Thisconfiguration can prevent an electrical connection (e.g., sparking)between distal portion 180 and chamber 160.

In another embodiment, shown in FIG. 8, the catalyst can be formed froma plurality of electrically conductive segments 190 separated by andmechanically connected to a plurality of electrically non-conductivesegments 195. In this embodiment, the catalyst can extend through theignition port between a point inside the cavity and another pointoutside the cavity, but the electrically discontinuous profilesignificantly prevents sparking and energy leakage.

Another method of forming a plasma consistent with this inventionincludes subjecting a gas in a cavity to electromagnetic radiationhaving a frequency less than about 333 GHz in the presence of an activeplasma catalyst, which generates or includes at least one ionizingparticle.

An active plasma catalyst consistent with this invention can be anyparticle or high energy wave packet capable of transferring a sufficientamount of energy to a gaseous atom or molecule to remove at least oneelectron from the gaseous atom or molecule in the presence ofelectromagnetic radiation. Depending on the source, the ionizingparticles can be directed into the cavity in the form of a focused orcollimated beam, or they may be sprayed, spewed, sputtered, or otherwiseintroduced.

For example, FIG. 9 shows radiation source 200 directing radiation intoradiation chamber 205. Plasma cavity 210 is positioned inside of chamber205 and may permit a gas to flow therethrough via ports 215 and 216.Source 220 can direct ionizing particles 225 into cavity 210. Source 220can be protected, for example, by a metallic screen which allows theionizing particles to pass through but shields source 220 fromradiation. If necessary, source 220 can be water-cooled.

Examples of ionizing particles consistent with this invention caninclude x-ray particles, gamma ray particles, alpha particles, betaparticles, neutrons, protons, and any combination thereof. Thus, anionizing particle catalyst can be charged (e.g., an ion from an ionsource) or uncharged and can be the product of a radioactive fissionprocess. In one embodiment, the vessel in which the plasma cavity isformed could be entirely or partially transmissive to the ionizingparticle catalyst. Thus, when a radioactive fission source is locatedoutside the cavity, the source can direct the fission products throughthe vessel to ignite the plasma. The radioactive fission source can belocated inside the radiation chamber to substantially prevent thefission products (i.e., the ionizing particle catalyst) from creating asafety hazard.

In another embodiment, the ionizing particle can be a free electron, butit need not be emitted in a radioactive decay process. For example, theelectron can be introduced into the cavity by energizing the electronsource (such as a metal), such that the electrons have sufficient energyto escape from the source. The electron source can be located inside thecavity, adjacent the cavity, or even in the cavity wall. It will beappreciated by those of ordinary skill in the art that any combinationof electron sources is possible. A common way to produce electrons is toheat a metal, and these electrons can be further accelerated by applyingan electric field.

In addition to electrons, free energetic protons can also be used tocatalyze a plasma. In one embodiment, a free proton can be generated byionizing hydrogen and, optionally, accelerated with an electric field.

Multi-Mode Radiation Cavities

A radiation waveguide, cavity, or chamber can be designed to support orfacilitate propagation of at least one electromagnetic radiation mode.As used herein, the term “mode” refers to a particular pattern of anystanding or propagating electromagnetic wave that satisfies Maxwell'sequations and the applicable boundary conditions (e.g., of the cavity).In a waveguide or cavity, the mode can be any one of the variouspossible patterns of propagating or standing electromagnetic fields.Each mode is characterized by its frequency and polarization of theelectric field and/or the magnetic field vectors. The electromagneticfield pattern of a mode depends on the frequency, refractive indices ordielectric constants, and waveguide or cavity geometry.

A transverse electric (TE) mode is one whose electric field vector isnormal to the direction of propagation. Similarly, a transverse magnetic(TM) mode is one whose magnetic field vector is normal to the directionof propagation. A transverse electric and magnetic (TEM) mode is onewhose electric and magnetic field vectors are both normal to thedirection of propagation. A hollow metallic waveguide does not typicallysupport a normal TEM mode of radiation propagation. Even thoughradiation appears to travel along the length of a waveguide, it may doso only by reflecting off the inner walls of the waveguide at someangle. Hence, depending upon the propagation mode, the radiation (e.g.,microwave) may have either some electric field component or somemagnetic field component along the axis of the waveguide (often referredto as the z-axis).

The actual field distribution inside a cavity or waveguide is asuperposition of the modes therein. Each of the modes can be identifiedwith one or more subscripts (e.g., TE₁₀ (“tee ee one zero”). Thesubscripts normally specify how many “half waves” at the guidewavelength are contained in the x and y directions. It will beappreciated by those skilled in the art that the guide wavelength can bedifferent from the free space wavelength because radiation propagatesinside the waveguide by reflecting at some angle from the inner walls ofthe waveguide. In some cases, a third subscript can be added to definethe number of half waves in the standing wave pattern along the z-axis.

For a given radiation frequency, the size of the waveguide can beselected to be small enough so that it can support a single propagationmode. In such a case, the system is called a single-mode system (i.e., asingle-mode applicator). The TE₁₀ mode is usually dominant in arectangular single-mode waveguide. As the size of the waveguide (or thecavity to which the waveguide is connected) increases, the waveguide orapplicator can sometimes support additional higher order modes forming amulti-mode system. When many modes are capable of being supportedsimultaneously, the system is often referred to as highly moded.

A simple, single-mode system has a field distribution that includes atleast one maximum and/or minimum. The magnitude of a maximum largelydepends on the amount of radiation supplied to the system. Thus, thefield distribution of a single mode system is strongly varying andsubstantially non-uniform.

Unlike a single-mode cavity, a multi-mode cavity can support severalpropagation modes simultaneously, which, when superimposed, result in acomplex field distribution patter. In such a pattern, the fields tend tospatially smear and, thus, the field distribution usually does not showthe same types of strong minima and maxima field values within thecavity. In addition, as explained more fully below, a mode-mixer can beused to “stir” or “redistribute” modes (e.g., by mechanical movement ofa radiation reflector). This redistribution desirably provides a moreuniform time-averaged field distribution within the cavity.

A multi-mode cavity consistent with this invention can support at leasttwo modes, and may support many more than two modes. Each mode has amaximum electric field vector. Although there may be two or more modes,one mode may be dominant and has a maximum electric field vectormagnitude that is larger than the other modes. As used herein, amulti-mode cavity may be any cavity in which the ratio between the firstand second mode magnitudes is less than about 1:10, or less than about1:5, or even less than about 1:2. It will be appreciated by those ofordinary skill in the art that the smaller the ratio, the moredistributed the electric field energy between the modes, and hence themore distributed the radiation energy is in the cavity.

The distribution of plasma within a plasma cavity may strongly depend onthe distribution of the applied radiation. For example, in a pure singlemode system, there may only be a single location at which the electricfield is a maximum. Therefore, a strong plasma may only form at thatsingle location. In many applications, such a strongly localized plasmacould undesirably lead to non-uniform plasma treatment or heating (i.e.,localized overheating and underheating).

Whether or not a single or multi-mode cavity is used consistent withthis invention, it will be appreciated by those of ordinary skill in theart that the cavity in which the plasma is formed can be completelyclosed or partially open. For example, in certain applications, such asin plasma-assisted furnaces, the cavity could be entirely closed. See,for example, commonly owned, concurrently filed U.S. patent applicationSer. No. 10/______ (Atty. Docket No. 1837.0020), which is fullyincorporated herein by reference. In other applications, however, it maybe desirable to flow a gas through the cavity, and therefore the cavitymust be open to some degree. In this way, the flow, type, and pressureof the flowing gas can be varied over time. This may be desirablebecause certain gases, such as argon, which facilitate formation ofplasma, can be easier to ignite but may not be needed during subsequentplasma processing.

Mode-Mixing

For many plasma-assisted applications, a cavity containing a uniformplasma is desirable. However, because radiation can have a relativelylong wavelength (e.g., several tens of centimeters), obtaining a uniformdistribution can be difficult to achieve. As a result, consistent withone aspect of this invention, the radiation modes in a multi-mode cavitycan be mixed, or redistributed, over a period of time. Because the fielddistribution within the cavity must satisfy all of the boundaryconditions set by the inner surface of the cavity, those fielddistributions can be changed by changing the position of any portion ofthat inner surface.

In one embodiment consistent with this invention, a movable reflectivesurface can be located inside the radiation cavity. The shape and motionof the reflective surface should, when combined, change the innersurface of the cavity during motion. For example, an “L” shaped metallicobject (i.e., “mode-mixer”) when rotated about any axis will change thelocation or the orientation of the reflective surfaces in the cavity andtherefore change the radiation distribution therein. Any otherasymmetrically shaped object can also be used (when rotated), butsymmetrically shaped objects can also work, as long as the relativemotion (e.g., rotation, translation, or a combination of both) causessome change in the location or orientation of the reflective surfaces.In one embodiment, a mode-mixer can be a cylinder that is rotable aboutan axis that is not the cylinder's longitudinal axis.

Each mode of a multi-mode cavity may have at least one maximum electricfield vector, but each of these vectors could occur periodically acrossthe inner dimension of the cavity. Normally, these maxima are fixed,assuming that the frequency of the radiation does not change. However,by moving a mode-mixer such that it interacts with the radiation, it ispossible to move the positions of the maxima. For example, mode-mixer 38can be used to optimize the field distribution within cavity 12 suchthat the plasma ignition conditions and/or the plasma sustainingconditions are optimized. Thus, once a plasma is excited, the positionof the mode-mixer can be changed to move the position of the maxima fora uniform time-averaged plasma process (e.g., heating).

Thus, consistent with this invention, mode-mixing can be useful duringplasma ignition. For example, when an electrically conductive fiber isused as a plasma catalyst, it is known that the fiber's orientation canstrongly affect the minimum plasma-ignition conditions. It has beenreported, for example, that when such a fiber is oriented at an anglethat is greater than 60° to the electric field, the catalyst does littleto improve, or relax, these conditions. By moving a reflective surfaceeither in or near the cavity, however, the electric field distributioncan be significantly changed.

Mode-mixing can also be achieved by launching the radiation into theapplicator chamber through, for example, a rotating waveguide joint thatcan be mounted inside the applicator chamber. The rotary joint can bemechanically moved (e.g., rotated) to effectively launch the radiationin different directions in the radiation chamber. As a result, achanging field pattern can be generated inside the applicator chamber.

Mode-mixing can also be achieved by launching radiation in the radiationchamber through a flexible waveguide. In one embodiment, the waveguidecan be mounted inside the chamber. In another embodiment, the waveguidecan extend into the chamber. The position of the end portion of theflexible waveguide can be continually or periodically moved (e.g., bent)in any suitable manner to launch the radiation (e.g., microwaveradiation) into the chamber at different directions and/or locations.This movement can also result in mode-mixing and facilitate more uniformplasma processing (e.g., heating) on a time-averaged basis.Alternatively, this movement can be used to optimize the location of aplasma for ignition or other plasma-assisted process.

If the flexible waveguide is rectangular, a simple twisting of the openend of the waveguide will rotate the orientation of the electric and themagnetic field vectors in the radiation inside the applicator chamber.Then, a periodic twisting of the waveguide can result in mode-mixing aswell as rotating the electric field, which can be used to assistignition, modulation, or sustaining of a plasma.

Thus, even if the initial orientation of the catalyst is perpendicularto the electric field, the redirection of the electric field vectors canchange the ineffective orientation to a more effective one. Thoseskilled in the art will appreciated that mode-mixing can be continuous,periodic, or preprogrammed.

In addition to plasma ignition, mode-mixing can be useful duringsubsequent plasma processing to reduce or create (e.g., tune) “hot spotsin the chamber. When a radiation cavity only supports a small number ofmodes (e.g., less than 5), one or more localized electric field maximacan lead to “hot spots” (e.g., within cavity 12). In one embodiment,these hot spots could be configured to coincide with one or moreseparate, but simultaneous, plasma ignitions or processing events. Thus,the plasma catalyst can be located at one or more of those ignition orsubsequent processing positions.

Multi-Location Ignition

A plasma can be ignited using multiple plasma catalysts at differentlocations. In one embodiment, multiple fibers can be used to ignite theplasma at different points within the cavity. Such multi-point ignitioncan be especially beneficial when a uniform plasma ignition is desired.For example, when a plasma is modulated at a high frequency (i.e., tensof Hertz and higher), or ignited in a relatively large volume, or both,substantially uniform instantaneous striking and restriking of theplasma can be improved. Alternatively, when plasma catalysts are used atmultiple points, they can be used to sequentially ignite a plasma atdifferent locations within a plasma chamber by selectively introducingthe catalyst at those different locations. In this way, a plasmaignition gradient can be controllably formed within the cavity, ifdesired.

Also, in a multi-mode cavity, random distribution of the catalystthroughout multiple locations in the cavity increases the likelihoodthat at least one of the fibers, or any other passive plasma catalystconsistent with this invention, is optimally oriented with the electricfield lines. Still, even where the catalyst is not optimally oriented(not substantially aligned with the electric field lines), the ignitionconditions are improved.

Furthermore, because a catalytic powder can be suspended in a gas, eachpowder particle may have the effect of being placed at a differentphysical location within the cavity, thereby improving ignitionuniformity within the cavity.

Dual-Cavity Plasma Igniting/Sustaining

A dual-cavity arrangement can be used to ignite and sustain a plasmaconsistent with this invention. In one embodiment, a system includes atleast a first ignition cavity and a second cavity in fluid communicationwith the first cavity. To ignite a plasma, a gas in the first ignitioncavity can be subjected to electromagnetic radiation having a frequencyless than about 333 GHz, optionally in the presence of a plasmacatalyst. In this way, the proximity of the first and second cavitiesmay permit a plasma formed in the first cavity to ignite a plasma in thesecond cavity, which may be sustained with additional electromagneticradiation.

In one embodiment of this invention, the first cavity can be very smalland designed primarily, or solely for plasma ignition. In this way, verylittle radiation energy may be required to ignite the plasma, permittingeasier ignition, especially when a plasma catalyst is used consistentwith this invention.

In one embodiment, the first cavity may be a substantially single modecavity and the second cavity is a multi-mode cavity. When the firstignition cavity only supports a single mode, the electric fielddistribution may strongly vary within the cavity, forming one or moreprecisely located electric field maxima. Such maxima are normally thefirst locations at which plasmas ignite, making them ideal points forplacing plasma catalysts. It will be appreciated, however, that when aplasma catalyst is used, it need not be placed in the electric fieldmaximum and, many cases, need not be oriented in any particulardirection.

Illustrative Plasma-Assisted Processing in a Manufacturing Line

Methods and apparatus for plasma-assisted processing of work pieces in amanufacturing line may be provided. A plasma-assisted process caninclude any operation, or combination of operations, involving the useof a plasma. The work pieces can be plasma-processed continuously,periodically, in batches, in sequence, or any combination thereof.

Plasma-assisted processes consistent with this invention can include,for example, sintering, annealing, normalizing, spheroiding, tempering,age hardening, case hardening, or any other type of hardening or processthat involves heat-treatment. Plasma-assisted processing can alsoinclude joining materials that are the same or different from oneanother. For example, plasma-assisted processing can include brazing,welding, bonding, soldering, and other types of joining processes.Additional plasma-assisted processes, such as doping, nitriding,carburizing, decrystallizing, carbo-nitriding, cleaning, sterilizing,vaporizing, coating, and ashing, can also be included consistent withthis invention.

FIGS. 10-13 show various views of illustrative apparatus 300 forplasma-assisted sintering. It will be appreciated, however, thatapparatus 300 can be used to perform any other plasma-assisted processconsistent with this invention as well.

FIG. 10 shows a perspective view of illustrative apparatus 300 forplasma-assisted processing of one or more work pieces consistent withthis invention. Apparatus 300 can include, for example, radiation source305, radiation waveguide 307 through which radiation passes from source305 toward irradiation zone 325, and conveyor 310 for sequentiallymoving work pieces 320 into and out of irradiation zone 325 adjacentwaveguide 307. Apparatus 300 can also include one or more gas ports (notshown) for conveying a gas in, out, or through zone 325 to enable plasmaformation there.

FIG. 11 shows another perspective view of apparatus 300, taken alongline 11-11 of FIG. 10. Any of radiation source 305 and power supply 335(not shown) for powering source 305 can be located in housing 330. Itwill be appreciated, however, that source 305 and supply 335 can belocated anywhere in relation to the floor plan, or to meet any otherphysical or dimensional requirement, of plasma-assisted processingapparatus 300. This includes separating source 305 from supply 335, inor out of housing 330.

Source 305 can irradiate zone 325 from any direction. For example,radiation source 305 can be located above, below, or in the samehorizontal plane as zone 325 and waveguide 307 can be used to direct theradiation from source 305 to zone 325. If radiation source 305 iscapable of directing radiation in the form of a beam (e.g., a diverging,converging, or collimated beam), then waveguide 307 can be eliminatedand the zone can be irradiated simply by directing the radiation beamtoward zone 325. In another embodiment, source 305 can supply radiationto zone 325 via one or more coaxial cable (not shown). In yet anotherembodiment, the radiation output of source 305 can directly irradiatezone 325.

When apparatus 300 includes waveguide 307, waveguide can have anycross-sectional shape to selectively propagate any particular radiationmode or modes. For example, as shown in FIG. 10, waveguide 307 can havea rectangular cross-section, but could also have a round, oval, or othershape capable of propagating radiation. Also, waveguide 307 can belinear, arched, spiral, serpentine, or any other convenient form. Ingeneral, waveguide 307 can be used to couple radiation source 305 to aradiation zone (e.g., a cavity) for forming a plasma and performing anytype of plasma-assisted process.

A conveyor can include at least one carrier portion for conveying workpieces. As used herein, a carrier portion can be any portion of aconveyor adapted to carry, support, hold, or otherwise mount one or morework pieces. As shown in FIG. 11, for example, carrier portions 340 and342 can be circular plates on which one or more work pieces can beplaced and conveyed. FIG. 12, for example, shows a top plan view ofconveyor 310, including six holes 350 on which carrier portions 340 and342 can be positioned. Although conveyor 310 has been configured to holdup to six carrier portions, conveyor 310 can be configured to hold moreor less carrier portions, if desired. It will be appreciated that acarrier portion consistent with this invention can also be integral withthe conveyor or with the work piece.

Conveyor 310 need not include holes 350 consistent with this invention.For example, as shown in FIG. 14, upper surface 360 of conveyor 362 caninclude one or more recesses 364 in which one or more work pieces 366can be placed while conveyor 362 rotates or otherwise moves.Alternatively, a conveyor consistent with this invention can have raisedportions or even no surface features at all (not shown). That is, thesupporting surface of the or can be substantially flat and one or morework pieces can be placed in any convenient orientation on the surface.In this way, differently shaped work pieces can be used with the sameconveyor consistent with this invention.

Any number of work pieces can be carried by carrier portions consistentwith this invention. FIGS. 11 and 13, for example, show that carrierportions 340 and 342 each carry a single work piece. In this case, thework piece can be a powdered metal part to be sintered using a plasma.Also, as shown in FIG. 13, carrier portions 340 and 342 can beconfigured or shaped to fit in or otherwise attach to conveyor 310. Forexample, the sides of carrier portions 340 and 342 can be tapered sothat they precisely fit into holes 350. In addition, the upper surfaceof the carrier portions can be customized or otherwise adapted so thatone or more work pieces are carried or supported in a predeterminedposition. For this purpose, one or more adaptors can be used with thesame carrier portion so that it can be used for differently shaped workpieces and plasma-assisted processes.

A waveguide and at least one carrier portion can cooperate to form aplasma-processing cavity consistent with this invention. For example,FIG. 11 shows tip portion 370 of waveguide 307 facing downward at workpiece 320, which is located on carrier portion 342. Thus, work piece 320can be located between tip portion 370 and carrier portion 342 that,together, form cavity 369 (shown in FIG. 13) in which a plasma can beformed. It will be appreciated that cavity 369 can be open or closed andthe uopenness” of the cavity depends on the relative position of tipportion 370 with respect to carrier portion 342.

As shown in FIGS. 11 and 13, for example, work piece 320 can be liftedby carrier portion 342 toward tip portion 370 by actuator 372, makingthe size and openness of cavity 369 smaller. In one embodiment, the gapbetween tip portion 370 and carrier portion 342 is reduced such thatcavity 369 is essentially closed before a plasma is ignited, essentiallytrapping gas and forming a plasma with that gas. In another embodimentconsistent with this invention, a gap remains before, during, or afterplasma processing, permitting a gas to flow through the cavity.

In any case, cavity 369 can have the appropriate dimensions tosubstantially confine the plasma and prevent plasma formation outsidecavity 369. Thus, work pieces 320, which can be carried by carrierportions 340 and 342, can be conveyed sequentially into a plasmaprocessing station below tip 370 by rotating conveyor 310 with motor374.

To prevent gas and plasma from traveling up through waveguide 370,radiation-transmissive plate 373 (e.g., made from quartz or ceramic),can be used as shown in FIG. 13. In this case, plate 373 can act as anupper surface of plasma cavity 369. Waveguide tip 370 can include lip371, which may be cylindrical, conical, or any other shape configured toform a suitable plasma cavity. During operation, lips 371 can bepositioned around part 320 to form the sides of cavity 369. Finally,carrier portion 342, part 320, or conveyor 310 can be used to form thelower part of cavity 369. FIG. 11 illustrates how radiation 345 can bedirected toward part 320 into cavity 369 from waveguide tip 370. Inpractice, however, the distance between tip 370 and part 320 could bereduced to perform a plasma process, thereby making cavity 369 lessopen.

In another embodiment (not shown), a work piece can be lowered orotherwise positioned at a plasma-processing station using the carrierportion. And, once again, a processing cavity can be formed betweeneither the work piece or the carrier portion and a waveguide tip.Alternatively, as shown in FIG. 1, a plasma-processing cavity can beformed in a substantially radiation-transmissive vessel. In this case,neither the carrier portion nor the waveguide necessarily forms aportion of the plasma cavity. In another embodiment, the waveguidehousing can be replaced with a radiation-transmissive housing and usedto form a plasma cavity similar to the cavity shown in FIG. 1A, forexample. In other words, the waveguide need not be coupled directly tothe plasma-processing cavity. It can be coupled to a larger radiationcavity in which the plasma cavity is positioned.

Although work pieces can be carried into place by carrier portions,those work pieces need not carry or otherwise support the work piecesduring processing. That is, carrier portions can place the work piecesin a plasma cavity and then remove them from the cavity afterprocessing. The same or different carrier portions can also be used toremove the work pieces after they have been plasma-processed.

As used herein, a conveyor can be any device capable of moving workpieces from one location to another, and in particular to and from aplasma-processing station. Thus, in addition, or as an alternative, tothe rotatable table type conveyors shown in FIGS. 10-14, a conveyorconsistent with this invention can include, for example, a belt, atrack, a robot, a turntable, a roller, a wheel, a chain, a bucket, atray, a guide rail, a lift, a screw, a push bar, a ribbon screw, a railsystem, an under floor system, a roller system, a slider system, a slatsystem, a gravity feed system, a chain on edge system, a cable system, amagnetic conveyor, a pulley system, a reciprocating conveyor, or anyother moving and positioning mechanisms.

Conveyor 310, as well as plasma-processing cavity 325, can be located inradiation chamber 304 to prevent potentially harmful radiation fromescaping the processing station. Radiation chamber 304 can besubstantially reflective or otherwise opaque to the radiation suppliedby source 305 and being used to form the plasma. Chamber 304 can beparticularly useful when one or more of the components that form cavity325 are substantially transmissive to the radiation supplied by source305 or when cavity 325 is at least partially open. It will beappreciated, however, that if cavity 325 is sealed (e.g., by waveguidetip 370 and carrier portion 320) potentially harmful radiation can notescape cavity 325 during plasma-assisted processing and chamber 304 maybe redundant However, chamber 304 may still be used to trap theprocessing gas.

Apparatus 300 can include one or more ports for moving work pieces inand out of apparatus 300. For example, apparatus 300 can includeentrance port 380 for moving parts 320 into apparatus 300 forplasma-assisted processing. Entrance port 380 can be part of gas lock384 that substantially isolates a processing gas (e.g., argon, helium,nitrogen, etc.) in chamber 304 from a gas (e.g., air) outside chamber304. Similarly, apparatus 300 can include exit port 382 for removingparts 320 from apparatus 300 after plasma-assisted processing iscomplete. Exit port 382 can also be part of gas lock 386 thatsubstantially isolates the processing gas from the gas outside chamber304. Mechanical arms or guides (not shown) can be used to assist in theloading of parts onto, and the unloading of parts off of, conveyor 310,if desired.

As described more fully above, an active or passive plasma catalyst canbe used to ignite, modulate, or sustain a plasma at pressures below, at,or above atmospheric pressure consistent with this invention. Becausethese catalysts have already been described in detail above, they willnot be described again here. In addition, sparking devices, and otherdevices for inducing a plasma, can also be used consistent with thisinvention. In any case, the plasma catalyst can be placed in an operablelocation to relax, or improve, the plasma-ignition requirements. In oneembodiment, the plasma catalyst can be located on and carried by acarrier portion or the work piece itself. In another embodiment, theplasma catalyst can be attached or otherwise positioned adjacent towaveguide tip 370.

FIG. 15 shows a flow-chart for illustrative method 400 ofplasma-processing a plurality of work pieces consistent with thisinvention. The method can include: placing each of the plurality of workpieces in a plurality of movable carriers in step 405, sequentiallymoving each of the movable carriers on a conveyor into an irradiationzone in step 410, flowing a gas into the zone in step 415, igniting thegas in the zone by subjecting the gas to radiation to form a plasma instep 420, sustaining the plasma for a period of time sufficient toplasma-process at least one of the work pieces in the zone in step 425,and advancing the conveyor to move the at least one processed work pieceout of the zone in step 430.

A plasma-processing method consistent with this invention canselectively expose one or more of the work pieces to a plasma. Thisincludes exposing one or more work pieces for a relatively long periodof time compared to the others, or to a higher temperature plasma forthe same period of time, or a combination thereof. For example, as shownin FIG. 10, work pieces located in radiation zone 325 will be exposed toa plasma while the others work pieces within chamber 304, but not inzone 325, will not be so exposed. Moreover, the rate of rotation ofconveyor 310 can be varied or the length of time that a work pieceremains in zone 325 can be varied. Moreover, as shown in FIG. 11, theheight of carrier 342 and tip 370 can be varied to change the radiationintensity in zone 325 and therefore the plasma intensity there.

In one embodiment, an electric bias can be applied to one or more of thework pieces within an irradiation zone to produce a more uniform andrapid plasma-assisted process. For example, a potential difference canbe applied between an electrode (e.g., suspended in a plasma cavity) anda work piece. The work piece can be connected to a voltage sourcedirectly, or through one of the moveable carriers. The voltage sourcecan be outside the applicator or irradiation zone and the voltage can beapplied through a microwave filter to prevent, for example, microwaveenergy leakage. The applied voltage can, for example, take the form of acontinuous or pulsed DC or AC bias. In the case of a plasma-assistedcoating process, the applied voltage may attract charged ions,energizing them, and facilitate coating adhesion and quality.

In the foregoing described embodiments, various features are groupedtogether in a single embodiment for purposes of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed invention requires morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the followingclaims are hereby incorporated into this Detailed Description ofEmbodiments, with each claim standing on its own as a separate preferredembodiment of the invention.

1. A method of plasma-assisted processing a plurality of work pieces,the method comprising: placing each of the plurality of work pieces in aplurality of movable carriers; sequentially moving each of the movablecarriers on a conveyor into an irradiation zone; flowing a gas into theirradiation zone; igniting the gas in the irradiation zone to form aplasma; sustaining the plasma for a period of time sufficient to atleast partially plasma process at least one of the work pieces in theirradiation zone; and advancing the conveyor to move the at least oneplasma-processed work piece out of the irradiation zone.
 2. The methodof claim 1, wherein the plasma-processing is at least one of sintering,annealing, normalizing, spheroiding, tempering, age hardening, casehardening, joining, doping, nitriding, carburizing, decrystallizing,carbo-nitriding, cleaning, sterilizing, vaporizing, coating and ashing.3. The method of claim 1 wherein at least one of the work piecescomprises a plurality of parts to be joined.
 4. The method of claim 1,wherein the conveyor comprises at least one of a belt, a track, a robot,a turntable, a roller, a wheel, a chain, a bucket, a tray, a guide rail,a lift, a screw, a push bar, a ribbon screw, a rail system, an underfloor system, a roller system, a slider system, a slat system, a gravityfeed system, a chain on edge system, a cable system, a magneticconveyor, a pulley system, a reciprocating conveyor, and any othermechanism capable of moving the work pieces from one location toanother.
 5. The method of claim 1 wherein the work piece includes atleast one of a metal, a non-metal, a ceramic, a glass, an organicmaterial, and a non-organic material.
 6. The method of claim 1, whereinthe irradiation zone includes a housing for adjoining the carrier. 7.The method of claim 6, wherein the housing and the carrier cooperate toform a cavity.
 8. The method of claim 7, wherein the housing includes atleast a top portion.
 9. The method of claim 7, wherein the housingincludes an inlet for conveying gas to the cavity.
 10. The method ofclaim 6, further comprising moving the carrier to a position adjacentthe housing.
 11. The method of claim 6, further comprising moving thehousing to a position adjacent the carrier.
 12. The method of claim 1,further comprising igniting the plasma using a plasma catalyst.
 13. Themethod of claim 12, wherein the catalyst is at least one of an activecatalyst and a passive catalyst.
 14. The method of claim 13, wherein thecatalyst comprises at least one of metal, inorganic material, carbon,carbon-based alloy, carbon-based composite, electrically conductivepolymer, conductive silicone elastomer, polymer nanocomposite, and anorganic-inorganic composite.
 15. The method of claim 14, wherein thecatalyst is in the form of at least one of a nanoparticle, a nano-tube,a powder, a dust, a flake, a fiber, a sheet, a needle, a thread, astrand, a filament, a yarn, a twine, a shaving, a sliver, a chip, awoven fabric, a tape, and a whisker.
 16. The method of claim 15, whereinthe catalyst comprises carbon fiber.
 17. The method of claim 13, whereinthe catalyst is in the form of at least one of a nano-particle, anano-tube, a powder, a dust, a flake, a fiber, a sheet, a needle, athread, a strand, a filament, a yarn, a twine, a shaving, a sliver, achip, a woven fabric, a tape, and a whisker.
 18. The method of claim 13,wherein the plasma catalyst comprises an active plasma catalystincluding at least one ionizing particle.
 19. The method of claim 18,wherein the at least one ionizing particle comprises a beam ofparticles.
 20. The method of claim 18, wherein the particle is at leastone of an x-ray particle, a gamma ray particle, an alpha particle, abeta particle, a neutron, and a proton.
 21. The method of claim 18,wherein the at least one ionizing particle is a charged particle. 22.The method of claim 18, wherein the ionizing particle comprises aradioactive fission product.
 23. The method of claim 1, wherein thehousing comprises a waveguide.
 24. The method of claim 1, wherein atleast one of the plurality of work pieces is exposed to a substantiallylarger amount of plasma than other of the plurality of work pieces. 25.The method of claim 1, wherein the zone includes a housing thatcooperates with at least one of the plurality of work pieces to form acavity.
 26. The method of claim 1, wherein the sequentially movingincludes moving at least one of the movable carriers continuously. 27.The method of claim 1, wherein the sequentially moving includes moving aplurality of the movable carriers into the zone in batches.
 28. Themethod of claim 1, wherein the sustaining comprises directing an amountof electromagnetic radiation having a frequency less than about 333 GHzinto the zone.
 29. An apparatus for plasma-assisted processing aplurality of work pieces, the apparatus comprising: an electromagneticradiation source; a radiation housing through which radiation passesfrom the source to form a plasma from a gas; and a conveyor forsequentially moving the work pieces into and out of an irradiation zoneadjacent the housing.
 30. The apparatus of claim 29, further comprisinga plasma catalyst contained in the irradiation zone for igniting theplasma.
 31. The apparatus of claim 29, wherein the catalyst is at leastone of an active catalyst and a passive catalyst.
 32. The apparatus ofclaim 31, wherein the catalyst comprises at least one of metal,inorganic material, carbon, carbon-based alloy, carbon-based composite,electrically conductive polymer, conductive silicone elastomer, polymernanocomposite, and an organic-inorganic composite.
 33. The apparatus ofclaim 32, wherein the catalyst is in the form of at least one of anano-particle, a nano-tube, a powder, a dust, a flake, a fiber, a sheet,a needle, a thread, a strand, a filament, a yarn, a twine, a shaving, asliver, a chip, a woven fabric, a tape, and a whisker.
 34. The apparatusof claim 33, wherein the catalyst comprises carbon fiber.
 35. Theapparatus of claim 31, wherein the catalyst is in the form of at leastone of a nano-particle, a nano-tube, a powder, a dust, a flake, a fiber,a sheet, a needle, a thread, a strand, a filament, a yarn, a twine, ashaving, a sliver, a chip, a woven fabric, a tape, and a whisker. 36.The apparatus of claim 31, wherein the plasma catalyst comprises anactive plasma catalyst including at least one ionizing particle.
 37. Theapparatus of claim 36, wherein the at least one ionizing particlecomprises a beam of particles.
 38. The apparatus of claim 36, whereinthe particle is at least one of an x-ray particle, a gamma ray particle,an alpha particle, a beta particle, a neutron, and a proton.
 39. Theapparatus of claim 36, wherein the at least one ionizing particle is acharged particle.
 40. The apparatus of claim 36, wherein the ionizingparticle comprises a radioactive fission product.
 41. The apparatus ofclaim 29, wherein the conveyor includes at least one carrier portion forconveying the plurality of work pieces, and wherein the housing and theat least one carrier portion cooperate to form a cavity for at leastpartially containing the gas.
 42. The apparatus of claim 29, wherein thecarrier portion is movable relative to the housing.
 43. The apparatus ofclaim 29, wherein the housing includes a waveguide that couples theradiation zone to the radiation source.
 44. The apparatus of claim 29,wherein the conveyor comprises at least one of a belt, a track, a robot,a turntable, a roller, a wheel, a chain, a bucket, a tray, a guide rail,a lift, a screw, a push bar, a ribbon screw, a rail system, an underfloor system, a roller system, a slider system, a slat system, a gravityfeed system, a chain on edge system, a cable system, a magneticconveyor, a pulley system, a reciprocating conveyor, and any othermechanism capable of moving the work pieces from one location toanother.
 45. The apparatus of claim 29, wherein the conveyor includes atleast one movable carrier portion that is integrated with the conveyor.46. The apparatus of claim 29, wherein the conveyor comprises at leastone movable carrier portion, and wherein the irradiation zone comprisesa housing for temporarily adjoining to the carrier portion.
 47. Theapparatus of claim 36, wherein the housing and the at least one movablecarrier portion cooperate to form a temporary cavity.
 48. The apparatusof claim 29 further comprising a housing having at least a top portionto at least partially contain the plasma once formed.
 49. The apparatusof claim 29 wherein the conveyor comprises at least one carrier portion,the apparatus further comprising a housing that can move relative to theat least one carrier portion.
 50. The apparatus of claim 29, furthercomprising a plasma catalyst for igniting the plasma in the zone. 51.The apparatus of claim 29, further comprising a housing coupled to theradiation source with a waveguide to the zone.
 52. The apparatus ofclaim 29, wherein the zone includes a housing that cooperates with atleast one of the plurality of work pieces to form a cavity.
 53. Theapparatus of claim 29 further comprising a gas inlet for conveying thegas into the irradiation zone to enable plasma formation in theirradiation zone.
 54. A method of plasma-assisted processing a pluralityof work pieces, the method comprising: sequentially conveying aplurality of work pieces into an irradiation zone; flowing a gas intothe irradiation zone; igniting the gas in the irradiation zone to form aplasma; sustaining the plasma for a period of time sufficient to atleast partially plasma process at least one of the work pieces in theirradiation zone; and sequentially conveying the plurality of workpieces out of the irradiation zone.
 55. The method of claim 54, furthercomprising placing the plurality of work pieces on a plurality ofmovable carriers before sequentially conveying the plurality of workpieces into the irradiation zone.
 56. The method of claim 55, whereinthe irradiation zone includes a housing configured to adjoin at leastone of the plurality of carriers, and wherein the method furthercomprises forming a plasma cavity in the irradiation zone by moving thehousing and the at least one of the plurality of carriers closertogether.
 57. The method of claim 56, wherein the housing includes atleast a top portion, and wherein the moving comprises moving the atleast one of the plurality of carriers toward the top portion.
 58. Themethod of claim 56, wherein the housing includes at least a top portion,and wherein the moving comprises moving the top portion toward the atleast one of the plurality of carriers.
 59. The method of claim 54,wherein the igniting the gas comprises exposing the gas to theelectromagnetic radiation at a frequency less than about 333 GHZ in thepresence of a plasma catalyst at a gas pressure of at least aboutatmospheric pressure.
 60. The method of claim 59, wherein the plasmacatalyst is at least one of an active plasma catalyst and a passiveplasma catalyst.
 61. The method of claim 56, wherein the housingcomprises a waveguide.
 62. The method of claim 54, wherein thesequentially conveying into the irradiation zone is at least one ofcontinuous and batched.
 63. The method of claim 54, wherein theconveying comprises moving the work pieces along a manufacturing line.64. The method of claim 54, further comprising applying an electric biasto the work piece during the sustaining.
 65. The method of claim 64,wherein the applying comprises applying at least one of a DC bias, an ACbias, a pulsed bias, and a continuous bias.